Not denying bush mechanics are amazing with what they do and get away with .....and sometimes needs must ......I've rebuilt diffs and gearboxes in mud and dust where they failed .Not really a setup to test piezoelectric injectors as you need modulator with duty cycle etc but it isn't dangerous as long as you won't put your hand next to nozzle....he tested the spray pattern, he will test the resistance and that's about it, if ok put it back in. In 3rd world countries they make do with what they've got ,nothing wrong with that.